A common 25,000 dalton serine protease is associated with chromatin isolated from various tissues and also a protease appears to be closely associated with chromosome bands of Drosophila polytene chromosome. The chromosomal protease specifically cleaves only H1 histone when chomatin is supercoiled chromosome. Therefore, we like to investigate the possible effect of protease inhibitors on the heat specific puffing of polytene chromosome, RNA and DNA synthesis in thymus lymphocytes and also the turnover of chromosomal nonhistone proteins. The 25,000 dalton chromosomal protease will be purified by affinity chromatography and characterized.